Related on OB: Formative Youth
If you want people to repeat this back, write it in a test, maybe even apply it in an academic context, a four-credit undergrad course will work.
If you want them to have it as the ground state of their mind in everyday life, you probably need to have taught them songs about it in kindergarten.
There's been some discussion here on the formation of rationalist communities.
If you look at any large, well-established religious community, you will see an extraordinary amount of attention being paid to the way children are raised. This is hardly surprising, since upbringing is how new members enter the community. Far more people become Mormons because they were raised by Mormon parents than because they had a long talk with two guys in white shirts.
This doesn't seem to be the case in the rationalist community. Looking at how we all got here, I don't see all that many who were simply raised by rationalist parents, and had a leg up. Maybe this is a sampling bias -- a straightforward, enlightened upbringing is not as dramatic as a break from fundamentalist religion, and perhaps people don't think it's a story worth telling.
But I don't think we can count out the possibility that we're just not doing the job of passing on our memes. I can even see a few reasons why this might be the case. In mixed marriages, it is usually the more devout parent, and especially the parent from the more demanding religion, who has the say in raising the children. Thus, we see spouses convert to Catholicism, to Orthodox Judaism, to Mormonism, but rarely to Congregationalism, or Unitarianism. On this totem pole, atheism seems to be pretty much at the bottom.
And perhaps this also has something to do with the shyness of the atheist parent. Even in unmixed marriages, the unspoken thought seems to be "so, our children will become atheists just because their parents were atheists, just as Baptist children become Baptist because their parents were Baptist -- are we really any better?" We resent the idea of the religionists forcing their foolish memes on their children, and want ours to choose their own paths. We think if we just get out of the way, our children will do whatever is right for them, as though by doing this we could make them the ultimate source of their lives.
We have to make choices -- doing nothing is still a choice. There is nothing wrong with attempting to light our children's way to wisdom which took us time and effort to locate on our own.
(As always, please post one suggestion per comment so that voting can represent an individual judgment of that suggestion.)
(Disclaimer: I am not a parent, and am not remotely ready to become one. Nonetheless, I feel this could be a fruitful topic for discussion)
ETA: I hope it doesn't look like I'm simply asking how to raise atheists -- I'm setting the bar a bit higher than that. I speak of atheist parents in the latter part of the post simply because I have no data on avowedly rationalist parents.